Despite recent advances in the study of eukaroytic gene regulation, a major obstacle to the therapeutic management of human disease remains the site-specific expression of genes in vivo. In principle, genetically-engineered endothelial cells can be used to provide site-specific gene therapy for cardiovascular and other diseases. Endothelial cells play an important role in the pathogenesis of cardiovascular disease and in systemic atherosclerosis. These cells influence the integrity of the arterial wall, regulate thrombolysis, and modulate vascular smooth muscle cell tone. Because thromboses associated with atherosclerotic plaques are usually focal and represent injury to localized arterial segments, it is desirable to direct treatment to specific sites of injury. Genetically-modified endothelial or other vascular cells could be used to deliver anticoagulant, vasodilatory, angiogenic or growth factors in vivo. Because of their proximity to the circulation, they also have potential to treat systemic inborn inherited diseases. This approach may also provide a means to address basic questions of vascular biology. In this proposal, we develop a novel approach to the delivery of proteins to discrete arterial segments in vivo using endothelial or other vascular cells which have been genetically-modified. The Yucatan minipig has been chosen as an animal model for the development of site-specific gene therapy. Endothelial cells from the inbred Yucatan minipig will be infected with a replication-defective retroviral vector expressing recombinant beta- galactosidase. These infected cells will be introduced with a catheter into denuded illofemoral arteries of syngeneic animals. Arterial segments explanted 2 weeks to 12 months later will be examined. We have recently shown that endothelial cells expressing recombinant beta-galactosidase have successfully implanted on the vessel wall using this method. In this proposal, this technique will be optimized and used to introduce an angiogenic protein, basic fibroblast growth factor, into the arterial wall and to determine its biologic effect in situ. In addition, preliminary experiments indicate that retroviral vectors can be used to introduce recombinant genes to specific sites in the vasculature by direct infection. These techniques, providing for the transfer of endothelial cells and the expression of recombinant genes in the vasculature in vivo, may allow the introduction of proteins with therapeutic value in the management of cardiovascular, systemic, and other diseases.